This invention relates generally to centers for use in the machining art and relates more particularly to spring-loaded centers for maintaining a rotatable cutting tool, such a tapping tool or reamer, in axial alignment with a hole to be worked upon.
A spring-loaded center with which this invention is concerned includes an elongated body having a shank adapted to be mounted within the holder of a machine tool, such as the spindle of a drill, and defining a cavity opening out of the body opposite the shank end. A tipped centering pin is slidably mounted within the body cavity for movement between an extended position and a retracted position. A spring is interposed between the body and the centering pin for biasing the pin from the retracted position toward the extended position. Examples of centers of the aforedescribed type are described in U.S. Pat. Nos. 2,286,088; 3,653,780; 3,456,534 and 3,653,780.
To use the center, a rotatable cutting tool such as a tapping tool or reamer, is positioned in operative working relationship with a hole formed in a workpiece, and a machine tool holder is positioned in axial registry with the cutting tool. The center is then mounted within the machine tool holder, and the centering pin is operatively maneuvered into engagement with a recess or the like normally provided within an end of the cutting tool. The spring thereafter maintains the centering pin in constant engagement with the cutting tool as the tool moves axially through the hole. With the centering pin in constant engagement with the cutting tool, the holder of the machine tool is not required to be continually moved toward the workpiece as the tool moves axially along through the hole.
One limitation associated with prior art centers, such as those described in the referenced patents, relates to the fact that the centers include no means for holding the centering pins in a retracted condition. Therefore, it is not uncommon that while the center is manipulated into place with the cutting tool, one of the operator's hands is necessary for holding the pin in a retracted position. It would be desirable to provide a new and improved center wherein the centering pin can be locked in a retracted position so that the operator's hand which would ordinarily be required to hold the pin in a retracted position is free to perform other tasks.
It is an object of the present invention to provide a new and improved spring-loaded center of the aforedescribed type.
Another object of the present invention is to provide such a center having a centering pin which can be releasably secured in a retracted position.
Still another object of the present invention is provide such a center which is capable of being mounted within machine tool collets or similar holders of alternative sizes.
Yet another object of the present invention is to provide such a center which is designed to reduce the likelihood of wear upon its centering pin as the cutting tool is rotated relative to the machine tool holder within which the center is mounted.